APT IPv6 or IPv4 on Ubuntu/Debian
For force IPv6 or IPv4 you hav to use:
apt -o Acquire::ForceIPv6=true update
or
apt -o Acquire::ForceIPv4=true update
Ceate the file 99force-ipv6
in /etc/apt/apt.conf.d/
if you want it to be persistent.
#/etc/apt/apt.conf.d/99force-ipv6
Acquire::ForceIPv6 "true";